Shaped bodies with high temperature strength and corrosion resistance against moltenmetals particularly molten iron and steels



3 E. PIPITZ ETAL 3,398,923

SHAPE ODIES WITH HIGH T ERATURE STRENGTH AND CORROSION RE TANCE AGAINST MOL MET s PARTICULARLY MOLTEN IRON AND ELS Filed Nov. 19, 1965 2 Sheets-Sheet 1 Aug. 27, 1968 IRON AND STEELS Filed NOV. 19, 1965 E. PIPITZ ET AL 3,398,923 SHAPED BODIES WITH HIGH TEMPERATURE STRENGTH AND CORROSION RESISTANCE AGAINST MOLTEN METALS PARTICULARLY MOLTEN 2 Sheets-Sheet 2 1 N VEN TORS United States Patent "ice 3,398,923 SHAPED BODIES WITH HIGH TEMPERATURE STRENGTH AND CORRGSION RESlSTANCE AGAINST MOLTEN METALS PARTICULARLY MOLTEN IRON AND STEELS Egon Pipitz, Gerolf Strohmeier, and Karl Sedlatschek,

Reutte, Tyrol, Austria, assignors to Schwarzkopf Development Company, New York, N.Y., a corporation of New York Filed Nov. 19, 1965, Ser. No. 508,690 Claims priority, application Austria, Nov. 20, 1964, A 9,849/64; Dec. 7, 1964, A 10,332/64; Dec. 10, 1964, A 10,493/64 12 Claims. (Cl. 249134) This invention relates to shaped hard bodies having high resistance to molten metal and particularly to molten iron and steel, such as permanent molds, casting nozzles, casting stoppers for casting equipment, pouring lips of ladles, protective thermocouple enclosures and the like, which have to be exposed for a prolonged time to molten steel, iron and like metals having a high melting temperature such as 1525 C. and higher. Such bodies must combine the good corrosion resistance and scaling resistance of ceramics with the good mechanical strength and good electrical and thermal conductivity of metals. The best such heretofore available bodies have combined alumina ceramics with chromium of molybdenum or chromiummolybdenum alloys. However, such known bodies had only a short life caused by scaling and disintegration when exposed to molten metal such as molten iron or steel.

Among the objects of the invention are such shaped hard bodies which will remain intact and resist corrosion and scaling when exposed to such molten corrosive metal for a much longer useful life.

The foregoing and other objects of the invention ca best be understood in the followingdescription and exemplifications thereof in connection with the accompanying drawings wherein:

FIGURE 1 is a cross-sectional view of a simple example of permanent mold of the invention used for casting a steel body having the shape of the interior mold surface;

FIGURE 2 is a cross-sectional view of a valve-like molding outlet and associated stopper-like core body made with the compositions of the invention and being parts of a casting crucible or vessel of a known type continuous-steel-casting apparatus;

FIGURE 2A is a cross-sectional view of such casting inlet vessel of such apparatus; and

FIGURE 3 is a side view of a thermocouple unit showing in cross-section its protective thermocouple enclosure exemplifying the invention.

FIGURE 1 shows, as an example only, a permanent mold of the invention for casting and forming outof molten steel a simple cast steel structure having the shape of the interior surface 10-1 of such mold. Such and analogous mold structures of the invention will resist corrosion by the corrosive molten cast metal including permanent molds into which the molten metal is delivered under pressure or by centrifugal forces. Heretofore such permanent molds have been made of metal or metal alloys. However, the metal composition of such known permanent molds has in many cases a melting temperature not exceeding that of the cast molten metal. As a result, such known molds are subject to severe corrosion by the cast molten metal and have only a limited useful life. Although ceramic materials have a higher melting temperature than the cast molten metal, ceramic molds lack the required thermal stability when subjected to rapid temperature variations or thermal shocks.

3,398,923 Patented Aug. 27, 1968 In accordance with the invention, permanent molds or mold structure for casting metal bodies of corrosive molten metal are formed of fine powder particle compositions combining to 15 vol. percent (volume percent) of a zirconium oxide base ceramic phase containing 4 to 10 wt. percent of an additional ceramic consisting of magnesium oxide or calcium oxide or of both of these addition-a1 ceramics with 20 to vol. percent of high melting metal phase selected from molybdenum or tungsten or of both. For best results, the metallic phase should constitute 40 to 60 vol. percent of the mold, with 60 to 40 vol. percent of the balance consisting of zirconium oxide base ceramic as set forth below.

By selecting the proportions and content of the above specified ceramic and metal phases, the properties of the permanent mold of the invention may be modified to meet the specific operating requirements. The selected metallic and ceramic, phases should have a materially higher melting temperature than the to-be-cast molten metal. Where high stability under varying temperatures or thermal shocks is required, the metallic phase content will be made greater. Where the permanent mold is subjected to strong oxidizing action, its oxidation resistance is increased by adding chromium to the metal phase and by large ceramic phase content. The metallic phase may contain up to 50 wt. percent (weight percent) chromium. The oxide ceramic phase may further contain up to 50 wt. percent of its own weight of thoria (thorium oxide), hafnia (hafnium oxide) and titania (titanium oxide).

The shaped bodies according to the invention are best made by powdermetallurgical methods. The powdered starting materials are intimately mixed, pressed Within a die into the desired shape and subsequently sintered in a neutral or reducing atmosphere. The sintering may be effected in one or two stages. During the sintering of the composite materials consisting of the zirconia base ceramic and of molybdenum in the above specified proportions it proved possible to approach the theoretical density at sintering temperatures of only 1700 to 2100 C.

Shaped permanent casting molds of the invention formed of the above specified compositions when used in contact with molten metals in an oxidizing atmosphere have a higher order of resistance to corrosion and scaling than the best above described prior bodies. They are further distinguished by surprisingly good temperature stability or resistance to temperature variations or thermal shocks and by good thermal conductivity. Permanent mold bodies of the new above specified compositions exhibit resistance against corrosion and scaling when in contact with ferrous molten metals, such as steel or iron and also with molten non-ferrous metals, such as light metals and zinc.

Sintered permanent mold bodies of the compositions of the invention may be given the desired accurate final shape with conventional machining operations such as by a cutting tool or lathe, milling or drilling. Threads may be readily machined in such mold bodies. Large permanent mold bodies of the invention may be formed of several complementary sections which, after machining to final shape, are joined to each other into the desired large mold as by threaded interfitting junctions.

The oxidation resistance of the mold surfaces of permanent molds of the invention is increased by removing from the exposed mold-surface layer its metal content as with nitrohydrochloric acid and forming an exposed mold-surface layer consisting of a zirconium oxide skeleton which is free of metal and exhibits high resistance to wetting by the cast molten metal.

As an example, there will be described the process for producing a hollow permanent mold with a composition of the invention, such as a tubular mold centimeters long with an inner diameter of 10 centimeters and a wall thickness of 2 centimeters. Because of its great length, it seemed desirable to form such permanent mold of two longitudinal mold sections. There was prepared an intimate fine powder mixture consisting of 60 vol. percent molybdenum, 36 vol. percent zirconium oxide and 4 vol. percent magnesium oxide. This powder mixture was hydrostatically compressed into a self-supporting compact of the desired mold shape. The compact was then subjected to an initial sintering operation at 1200 C., followed by cooling both in a hydrogen. The presintered compact was then machined as with a cutting tool or by drilling. The presintered compact was thereafter subjected to the final sintering operation at 2000 C. in hydrogen. The fully sintered mold was then machined as with a cutting or drilling tool to the desired final shape. By etching the exposed mold surfaces, as with nitrohydrochloric acid, their metal content was removed thereby providing exposed mold surfaces formed of a zirconium oxide-base ceramic skeleton free from metal and not readily wetted by molten steel or other molten corrosive metals. Two such mold sections were thereafter joined along mating ends into the desired long permanent mold. Such junction was obtained by machining in the mating mold ends complementary screw threads and screwing them firmly together. The so formed mold of the desired length was thereafter enclosed with a tightly fitting steel enclosure. Such permanent molds of the invention have excellent resistance to thermal shock or rapid temperature variations.

FIGURE 2 shows in cross-section high temperature and corrosion resistant discharge nozzle like mold body 1 and associated stopper like body 2 of a molten metal discharge crucible or vessel, each being of conventional shape but formed of compositions of the invention described above which resists corrosion by molten steel and iron. The molding outlet nozzle 1 has a discharge passage 1-2 with a conically shaped smooth inlet surface 1-3. The cooperating stopper-like mold core 2 has a downwardly facing smooth conical surface 2-3 defining with the conical nozzle mold surface 1-3 an inlet for the narrower end section of the mold discharge passage. Both the corrosion resistant mold nozzle 1 and the associated corrosion resistant mold core 2 are formed by powdermetallurgical methods out of the above described compositions of the invention. In this specific example, both the mold 1 and the mold core 2 are formed of a sintered compacted body consisting of a 60 vol. percent molybdenum, 26 vol. percent zirconia and 4 vol. percent magnesium oxide. Such sintered compact bodies may be readily given a final shape by knowing machining processes such as turning on a lathe or other analogous machining operations. After machining the conical surface 1-3 of the mold 1 and the cooperating conical surface 2-1 of the core 2 to the smooth final conical shape, the so machined facing conical surfaces 1-3 are treated to remove from their surface layers the metallic content. For example, in such metal removing surface treatment there may be used as nitrohydrochloric acid (aqua regia) which removes the molybdenum from the exposed surface layers 1-3 and 2-3 of the two bodies 1 and 2. Such removal of the molybdenum content provides the mold surface layer 1-3 and the cooperating core surface layer 2-3 with a ceramic skeleton structure which is firmly anchored to the respective underlying solid bodies of the mold 1 and its core 2. The two thus formed cooperating ceramic layers 1-3 and 2-3 of the discharge mold 1 and core 2 are free of any metallic content and as a result they are not readily wetted and exhibit high corrosion resistance to molten steel, iron or like corrosive liquids.

FIGURE 2A shows the casting crucible forming part of a continuous steel casting apparatus of a type known in the art by which molten metal cast into the crucible is formed or extruded into a continuously moving solidified elongated steel body. The crucible 4 has a body of 4 which are formed of a material which resists corrosion by molten steel. The molten steel which is to be formed by such apparatus is discharged onto section 6 of the interior surface of the bottom crucible wall 5. The discharged molten steel impinging upon inner surface section 6 of the crucible subjects this crucible section 6 to very severe corroding action. In accordance with the invention this interior crucible bottom wall section 6 is formed of a composition of the invention. As an example, this crucible wall section is formed of acorrosion resistive composition consisting of 45 vol. percent molybdenum, 5 vol. percent chromium, 45 vol. percent chromium oxide and 5 vol. percent magnesium oxide. To this end a thorough mixture of fine powder particles of these ingredients is. compacted, as by hydrostatic pressure, within known-type suitable dies to form compacted bodies having the shape of the desired nozzle 1 and stopper 2. The so formed body compacts are then sintered for one hour in hydrogen at 2000 C. yielding strong shaped nozzle and stopper bodies with a density near the theoretical limit. After cooling in a similar atmosphere to normal temperature, the resulting nozzle and stopper bodies can be easily machined to final desired shape, as by turning on a lathe or analogous machining operations. In the case of mold 1 and its core 2, machining is applied to form their facing respective conical surfaces 1-3 and 2-3. The core 2 has also machined therein a thread 2-4 for affixing thereto the end portion of a conventional actuating rod 7 serving to move to its proper spacing from its facing conical mold surface 1-3.

As another example, there will be described how a protective thermocouple sheath or enclosure is formed with a composition of the invention which protects it when immersed in molten corrosive metal, such as molten steel or iron for measuring its temperature. There is prepared an intimately mixed powder mixture consisting of 65 vol. percent molybdenum powder, 31.5 vol. percent fine zirconia powder (ZrO and 3.5 vol. percent fine magnesium powder. The powder mixture is then compacted into round bars, as by hydrostatic pressing. The so formed compacted bar is sintered for an hour in hydrogen at 2000 C., yielding a sintered bar with a density near the theoretical limit of the composition. Such sintered bar has approximately the same thermal conductivity as carbon steel. Such sintered bar can be easily machined by turning or drilling into the final shape. Such thermocouple sheath not only has excellent resistance to corrosion when exposed to molten steel, but has also excellent resistance to thermal shock. Crack formations could not be observed in such thermocouple sheath after repeated quenching from a raised temperature of 1700 C. in water.

FIGURE 3 shows partially in cross-section and partially in elevation one example of a protective thermocouple enclosure of the invention. It has an; upper or exterior conventional tubular part 11 with a tube head 12 which does not come in direct contact wth the molten steel or molten corrosive glass, and which may be formed of steel, for instance. To the lower end of the hollow upper tube 11 is tightly afiixed, as by a threaded metal collar 13, the inner tubular protective tube enclosure 14 which is held immersed in the molten corrosive metal for protecting the thermocouple and its wire connection held in the hollow interior 17 of this thermocouple enclosure 14. This enclosure 14 is made of the composition of the invention combining a ceramic phase with a metal phase as described above. The upper metal tube 11 is likewise hollow and has two tubular connectors 15, 16 for circulating through its interior a cooling fluid such as water which suppresses excessive rise of its temperature by heat conveyed thereto from its immersed thermocouple enclosure tube 14.

Protective thermocouple enclosures of the invention are of great value for continuously measuring the temperature of molten steel and iron. They are'also of value for measuring the temperature of other molten metals,

such as molten aluminum, molten zinc, molten magnesium and also in nonmetallic corrosive molten substances, such as, for example, molten glass. The thermocouple protective tubes are also used in measuring the temperature of corrosive gases, for example, atmospheres which contain dry chlorine gas.

The principles underlying the invention described in connection with specific exemplifications will suggest other modifications and applications thereof. It is accordingly desired that the appended claims shall not be limited to specific examples shown or described herein.

There is claimed:

1. A shaped hard body of homogeneous composition of high temperature strength and resistance to corrosion by molten iron or steel and consisting of a ceramic phase and a metal phase,

said ceramic phase constituting 80 to vol. percent of said body and consisting of a ceramic selected from the group consisting of zirconium oxide containing 4 to 10 wt. percent of calcium oxide, zirconium oxide containing 4 to 10 wt. percent of magnesium oxide, zirconium oxide containing up to 50% thorium oxide, zirconium oxide containing up to 50% titanium oxide and having combinations of two and more of said ceramics,

said metallic phase constituting to 85 vol. percent of and being the balance of said body and consisting of metal selected from the group consisting of molybdenum, tungsten, molybdenum containing up to 50% chromium, tungsten containing up to 50% chromium, a tungsten-molybdenum alloy containing up to 50% chromium and mixtures of two and more of said metals,

said body consisting of a homogeneous mixture of fine powder particles of said specified ceramic and metal phase ingredients, which particles have been compacted and have been sintered at temperatures of at least 1800 C. into a body having a high density near the theoretical density of its composition and resisting corrosion by molten metal at high temperatures of at least about 1400 C. in contact therewith.

2. A shaped body as claimed in claim 1,

said ceramic phase being 60 to 40 vol. percent and said metal phase being 40 to 60 vol. percent of said shaped body.

3. A shaped body as claimed in claim 1,

the surface layer of the said body section exposed at said temperatures to said corrosive molten metal being free of said metal phase and being formed solely of said ceramic phase ingredients and exhibiting wetting resistance to said molten metal at said high temperature.

4. A shaped body as claimed in claim 1,

the surface layer of the said body section exposed at said temperatures to said corrosive molten metal being free of said metal phase and being formed solely of said ceramic phase ingredients and exhibiting wetting resistance to said molten metal at said high temperature,

said ceramic phase being 60 to 40 vol. percent and said metal phase being 40 to 60 vol. percent of said shaped body. 5. A shaped body as claimed in claim 1, said body having been compacted and sintered into a hollow body and resisting corrosion by molten metal when held in engagement with a surface of said body,

the surface layer of the said body section exposed at said temperatures to the said corrosive molten metal being free of said metal phase and being formed solely of said ceramic phase ingredients and exhibiting wetting resistance to said molten metal at said high temperature.

6. A shaped body as claimed in claim 1,

said body having been compacted and sintered into a hollow body and resisting corrosion by molten metal when held in engagement with a surface of said body,

the surface layer of the said body section exposed at said temperatures to the said corrosive molten metal being free of said metal phase and being formed solely of said ceramic phase ingredients and exhibiting wetting resistance to said molten metal at said high temperature,

said ceramic phase being 60 to 40 vol. percent and said metal phase being 40 to 60 vol. percent of said shaped body.

7. A hollow permanent mold for casting molten metal and forming shaped metal bodies, which mold has high resistance to thermal shock and consists of a ceramic phase and a metal phase,

said ceramic phase constituting to 15 vol. percent of said body and consisting of a ceramic selected from the group consisting of zirconium oxide containing 4 to 10 wt. percent calcium oxide, zirconium oxide containing 4 to 10 wt. percent magnesium oxide, such zirconium oxide containing up to 50 wt. percent thorium oxide, such zirconium oxide containing up to 50 wt. percent titanium oxide and combinations of two and more of said ceramics,

said metallic phase constituting 20 to vol. percent of and being the balance of said body and consisting of metal selected from the group consisting of molybdenum, tungsten, molybdenum containing up to 50 wt. percent chromium, tungsten containing up to 50 wt. percent chromium, a tungsten-molybdenum alloy containing up to 50 wt. percent chromium and mixtures of two and more of said metals,

said mold consisting of a homogeneous mixture of fine powder particles of said specified ceramic and metal phase ingredients, which particles have been compacted and have been sintered at temperatures of at least 1800 C. into a body having a high density near the theoretical density of its composition and resisting thermal variations and corrosion by molten metal at high temperatures of at least about 1400 C. in contact therewith.

8. A permanent mold as claimed in claim 7,

said ceramic phase being 60 to 40 vol. percent and said metal phase being 40 to 60 vol. percent of said mold.

9. A permanent moiu as claimed in claim 7,

the interior surface layer of the said mold exposed at said temperatures to said corrosive molten metal being free of said metal phase and being formed solely of said ceramic phase ingredients and exhibiting wetting resistance to said molten metal at said high temperature.

10. A permanent mold as claimed in claim 7,

the interior surface layer of the said mold exposed at said temperatures to said corrosive molten metal being free of said metal phase and being formed solely of said ceramic phase ingredients and exhibiting wetting resistance to said molten metal at said high temperature,

said ceramic phase being 60 to 40 vol. percent and said metal phase being 40 to 60 vol. percent of said shaped mold.

11. A permanent mold as claimed in claim 7,

said mold having been compacted and sintered into a hollow body and resisting corrosion by molten metal when held in engagement with an interior surface of said mold,

the interior surface layer of said mold exposed at said temperatures to the said corrosive molten metal being free of said metal phase and being formed solely of said ceramic phase ingredients and exhibiting wetting resistance to said molten metal at said high temperature.

12. A permanent mold as claimed in claim 7,

said mold having been compacted and sintered into a Q the interior surface layer of the said mold section exposed at said temperatures to the, said corrosive molten metal being free of said metal phase and being formed solely of said ceramic phase ingredients and exhibiting wetting resistance to said molten metal at said high temperature,

. said ceramiophase being 60 to- 40 vol. percent and said metal phase being 40 to 60 vol. percent of said mold. 1.:

References Cited, J UNITED STATES PATENTS Carlton et a1. 75206 X Iredell et a1. 75-206 Gatti 75206 Vordahl l. 75-206 Hay 1os s7 X Weber 105-57 x 10 I. SPENCER OVERHOLSER, Primary Examiner.

E. MAR, Assistant Examiner. 

7. A HOLLOW PERMANENT MOLD FOR CASTING MOLTEN METAL AND FORMING SHAPED METAL BODIES, WHIH MOLD HAS HIGH RESISTANCE TO THERMAL SHOCK AND CONSISTS OF A CERAMIC PHASE AND A METAL PHASE, SAID CERAMIC PHASE CONSTITUTING 80 TO 15 VOL. PERCENT OF SAID BODY AND CONSISTING OF A CERAMIC SELECTED FROM THE GROUP CONSISTING OF ZIRCONIUM OXIDE CONTAINING 4 TO 10 WT. PERCENT CALCIUM OXIDE, ZIRCONIUM OXIDE CONTAINING 4 TO 10 WT. PERCENT MAGNESIUM OXIDE, SUCH ZIRCONIUM OXIDE CONTAINING UP TO 50 WT. PERCENT THORIUM OXIDE, SUCH ZIRCONIUM OXIDE CONTAINING UP TO 50 WT. PERCENT TITANIUM OXIDE AND COMBINATIONS OF TWO AND MORE OF SAID CERAMICS, SAID METALLIC PHASE CONSTITUTING 20 TO 85 VOL. PERCENT OF AND BEING THE BALANCE OF SAID BODY AND CONSISTING OF METAL SELECTED FROM THE GROUP CONSISTING OF MOLYBDENUM, TUNGSTEN, MOLYBDENUM CONTAINING UP TO 50 WT. PERCENT CHROMIUM, TUNGSTEN CONTAINING UP TO 50 WT. PERCENT CHROMIUM, A TUNGSTEN-MOLYBDENUM ALLOY CONTAINING UP TO 50 WT. PERCENT CHROMIUM AND MIXTURES OF TWO AND MORE OF SAID METALS, SAID MOLD CONSISTING OF A HOMOGENEOUS MIXTURE OF FINE POWDER PARTICLES OF SAID SPECIFIED CERAMIC AND METAL PHASE INGREDIENTS, WHICH PARTICLES HAVE BEEN COMPACTED AND HAVE BEEN SINTERED AT TEMPERATURES OF AT LEAST 1800* C. INTO A BODY HAVING A HIGH DENSITY NEAR THE THEORETICAL DENSITY OF ITS COMPOSITION AND RESISTING THERMAL VARIATIONS AND CORROSION BY MOLTEN METAL AT HIGH TEMPERATURES OF AT LEAST ABOUT 1400* C. IN CONTACT THEREWITH. 